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From a7453aeeb398d6cbb7a709c4e2a1d75905220fff Mon Sep 17 00:00:00 2001
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From: Stanislav Zidek <szidek@redhat.com>
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Date: Fri, 16 Apr 2021 19:14:18 +0200
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Subject: [PATCH] pam_userdb: Prevent garbage characters from db
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Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1791965
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---
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modules/pam_userdb/pam_userdb.8.xml | 3 +-
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modules/pam_userdb/pam_userdb.c | 56 +++++++++++++++++------------
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2 files changed, 36 insertions(+), 23 deletions(-)
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diff --git a/modules/pam_userdb/pam_userdb.8.xml b/modules/pam_userdb/pam_userdb.8.xml
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index fa628ada..bce92850 100644
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--- a/modules/pam_userdb/pam_userdb.8.xml
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+++ b/modules/pam_userdb/pam_userdb.8.xml
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@@ -100,7 +100,8 @@
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</term>
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<listitem>
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<para>
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- Print debug information.
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+ Print debug information. Note that password hashes, both from db
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+ and computed, will be printed to syslog.
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</para>
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</listitem>
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</varlistentry>
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diff --git a/modules/pam_userdb/pam_userdb.c b/modules/pam_userdb/pam_userdb.c
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index dc2ca232..d59801bf 100644
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--- a/modules/pam_userdb/pam_userdb.c
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+++ b/modules/pam_userdb/pam_userdb.c
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@@ -194,7 +194,7 @@ user_lookup (pam_handle_t *pamh, const char *database, const char *cryptmode,
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}
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if (data.dptr != NULL) {
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- int compare = 0;
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+ int compare = -2;
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if (ctrl & PAM_KEY_ONLY_ARG)
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{
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@@ -209,36 +209,48 @@ user_lookup (pam_handle_t *pamh, const char *database, const char *cryptmode,
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char *cryptpw = NULL;
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if (data.dsize < 13) {
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- compare = -2;
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+ /* hash is too short */
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+ pam_syslog(pamh, LOG_INFO, "password hash in database is too short");
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} else if (ctrl & PAM_ICASE_ARG) {
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- compare = -2;
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+ pam_syslog(pamh, LOG_INFO,
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+ "case-insensitive comparison only works with plaintext passwords");
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} else {
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+ /* libdb is not guaranteed to produce null terminated strings */
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+ char *pwhash = strndup(data.dptr, data.dsize);
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+
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+ if (pwhash == NULL) {
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+ pam_syslog(pamh, LOG_CRIT, "strndup failed: data.dptr");
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+ } else {
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#ifdef HAVE_CRYPT_R
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- struct crypt_data *cdata = NULL;
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- cdata = malloc(sizeof(*cdata));
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- if (cdata != NULL) {
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- cdata->initialized = 0;
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- cryptpw = crypt_r(pass, data.dptr, cdata);
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- }
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+ struct crypt_data *cdata = NULL;
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+ cdata = malloc(sizeof(*cdata));
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+ if (cdata == NULL) {
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+ pam_syslog(pamh, LOG_CRIT, "malloc failed: struct crypt_data");
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+ } else {
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+ cdata->initialized = 0;
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+ cryptpw = crypt_r(pass, pwhash, cdata);
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+ }
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#else
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- cryptpw = crypt (pass, data.dptr);
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+ cryptpw = crypt (pass, pwhash);
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#endif
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- if (cryptpw && strlen(cryptpw) == (size_t)data.dsize) {
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- compare = memcmp(data.dptr, cryptpw, data.dsize);
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- } else {
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- compare = -2;
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- if (ctrl & PAM_DEBUG_ARG) {
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- if (cryptpw)
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- pam_syslog(pamh, LOG_INFO, "lengths of computed and stored hashes differ");
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- else
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- pam_syslog(pamh, LOG_INFO, "crypt() returned NULL");
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+ if (cryptpw && strlen(cryptpw) == (size_t)data.dsize) {
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+ compare = memcmp(data.dptr, cryptpw, data.dsize);
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+ } else {
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+ if (ctrl & PAM_DEBUG_ARG) {
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+ if (cryptpw) {
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+ pam_syslog(pamh, LOG_INFO, "lengths of computed and stored hashes differ");
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+ pam_syslog(pamh, LOG_INFO, "computed hash: %s", cryptpw);
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+ } else {
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+ pam_syslog(pamh, LOG_ERR, "crypt() returned NULL");
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+ }
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+ }
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}
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- }
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#ifdef HAVE_CRYPT_R
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- free(cdata);
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+ free(cdata);
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#endif
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+ }
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+ free(pwhash);
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}
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-
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} else {
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/* Unknown password encryption method -
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--
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2.30.2
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